Boulder Colorado Weather by Month: Normals and What to Expect

May 24, 2026 · 4 min read · boulder colorado monthly weather climate normals seasonal weather colorado climate front range weather ·

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How to Read Boulder's Climate by Month

Boulder's weather doesn't follow a smooth seasonal curve. Chinook winds erase winter for days at a time, monsoon thunderstorms compress summer rainfall into July and August afternoons, and the spring transition runs from late February through May with heavy snow possible any time in that window. The monthly figures below come from the NOAA 1991–2020 U.S. Climate Normals for the Boulder observing station, cross-checked against the NOAA Boulder Physical Sciences Laboratory daily records archive. Higher-elevation neighborhoods like Mapleton Hill and South Boulder run 2–4°F cooler with 10–20% more snow than the official station.

January

Average high 45°F, average low 22°F, precipitation 0.7 inches, snowfall 8 inches. The coldest month on average, but also the month most prone to Chinook events that lift the city to 60°F+ for 24–48 hours. Multi-day arctic outbreaks tied to Canadian air masses drop the city below 0°F two or three times per decade.

February

Average high 48°F, average low 24°F, precipitation 0.7 inches, snowfall 8 inches. Statistically similar to January but with longer daylight and a higher Chinook frequency. February is the start of the wildfire shoulder season when downslope winds dry fine fuels.

March

Average high 54°F, average low 28°F, precipitation 1.6 inches, snowfall 13 inches. Boulder's snowiest month on average. Upslope storms behind cold-front passages can drop 1–3 ft of heavy wet snow on a single event. Spring is at least four weeks away.

April

Average high 60°F, average low 33°F, precipitation 2.2 inches, snowfall 7 inches. Highly variable — 70°F days alternate with heavy late-season snow. The 2009 mid-April blizzard dropped 24+ inches; most years see at least one significant snow event.

May

Average high 69°F, average low 42°F, precipitation 2.7 inches, snowfall 1 inch. The wettest month on average, driven by Front Range upslope storms before the monsoon transition. Last spring freeze typically lands in early May; gardeners hold off planting frost-tender crops until mid-month.

June

Average high 79°F, average low 51°F, precipitation 2.0 inches, snowfall trace. Reliable warmth arrives, but afternoon thunderstorms become routine. Hail risk peaks in June across the Front Range plains. The dry foothills above the city set up for the wildfire-season peak.

July

Average high 87°F, average low 57°F, precipitation 2.0 inches, snowfall 0. The hottest month on average, with 5–10 days above 90°F. Monsoon moisture from the Gulf of California arrives mid-month, producing daily afternoon thunderstorms over the foothills and occasional flash flooding in the canyons.

August

Average high 85°F, average low 56°F, precipitation 1.7 inches, snowfall 0. Monsoon pattern continues. Severe thunderstorms with damaging wind and hail are most common in late afternoon. Wildfire risk remains elevated until the pattern breaks in early September.

September

Average high 76°F, average low 47°F, precipitation 1.7 inches, snowfall 1 inch. Boulder's most volatile month — the September 2013 flood and the September 2020 Cameron Peak fire growth both happened in this window. Early-season snow at higher elevations is routine; the first freeze typically arrives the first week of October.

October

Average high 63°F, average low 36°F, precipitation 1.3 inches, snowfall 4 inches. Aspen viewing peaks in the second and third weeks. First measurable snow at the city station typically arrives mid-month, though the 2019 October cold snap dropped to –1°F on October 30.

November

Average high 52°F, average low 28°F, precipitation 1.0 inches, snowfall 8 inches. Winter pattern locks in. The NWS Denver/Boulder office issues the first High Wind Warnings of the season as Chinook events become common. Cold-air pooling on still mornings is a recurring inversion pattern in Frasier Meadows and the South Boulder Creek corridor.

December

Average high 46°F, average low 23°F, precipitation 0.8 inches, snowfall 9 inches. Coldest sunrise temperatures of the year. The December 2021 Marshall Fire — Colorado's most destructive wildfire by structure count — burned under 100+ mph Chinook winds on December 30, demonstrating that the city's wildfire season has no true off-season when downslope wind patterns set up.